1. Field of the Invention
The present invention relates to a suitable spring connector used in, for example, a battery terminal of a cellular phone terminal, and to a terminal device including the spring connector.
2. Description of the Related Art
Hitherto, in an electronic device, such as a cellular phone terminal, a spring connector is mounted to a surface of a principle circuit board when an electrical component at, for example, a partial circuit board or a battery is connected to the principle circuit board. A spring connector is mounted by pushing a terminal electrode of the electrical component against a movable end that is urged by a spring. By this, electrical connection is achieved.
FIGS. 10 and 11 each show an example of a related spring connector. FIG. 11 shows the entire structure of a spring connector 40. FIG. 10 is a vertical sectional view taken along line X-X in FIG. 11. As shown in FIG. 10, in the spring connector 40, a plunger 11 and a coil spring 12 are accommodated in a tube 13 having a hollow interior. The plunger 11, the coil spring 12, and the tube 13 are formed of conductive metal. In the tube 13, a base portion 13a has a somewhat large diameter, and a bottom portion 13c of a circular hollow cylinder 13b is formed in the base portion 13a so as to have a conical shape. A coil spring 12 is disposed at a base-end side (bottom-portion-13c side) of the interior of the hollow cylinder 13b. The plunger 11 is disposed at a front-end side of the interior of the hollow cylinder 13b. The plunger 11 has a large-diameter portion 11a, which fits in the hollow cylinder 13b, and a small-diameter portion 11b, whose front end is exposed from the tube 13. A front end 13d of the tube 13 is narrowed. A stepped portion 11c, disposed between the large-diameter portion 11a and the small-diameter portion 11b of the plunger 11, engages with and is stopped by the front end 13d of the tube 13 to accommodate the plunger 11 in the tube 13.
The coil spring 12 is disposed in a compressed state in the tube 13, and pushes up the plunger 11 towards the front (the top in FIG. 10). In the spring connector 40 having such a structure, conduction is achieved by contact at a contact 1, a contact 2, and a contact 3. Accordingly, the plunger 11 and the tube 13 are in electrical conduction. The contact 1 is where the plunger 11 contacts an inside diameter portion of the tube 13. The contact 2 is where the coil spring 12 and the tube 13 contact each other. The contact 3 is where the plunger 11 and the coil spring 12 contact each other.
Therefore, the base portion 13a of the tube 13 is connected to a circuit board (not shown), and an end of the small-diameter portion 11b of the plunger 11 is brought into contact with a predetermined portion, such as a conductive portion of a battery, to achieve electrical connection.
In this case, the plunger 11 can be pushed into the interior of the tube 13 in correspondence with an amount by which the coil spring 12 can be compressed.
Japanese Unexamined Patent Application Publication No. 2004-192968 (Patent Document 1) discusses an example of this type of spring connector. Patent Document 1 discusses a structure in which a stable conductive path is provided by increasing the length of the coil spring pushing out the plunger.